The present invention relates to a video balun and more particularly, to a toolless video balun that allows quick connection to a network line without tools, and assures positive positioning of the BNC connector in between the top cover shell and the bottom cover shell.
For long distance transmission (about 100˜200 foot) of audio/video signal or data to prevent common-mode interference, the most economic way is to transmit signal in a balanced manner through a network line of impedance about 120-ohm between the two sides. However, a regular signal source is a balanced signal of impedance about 75-ohm. Therefore, the signal must be converted from 75-ohm into 120-ohm before transmission. In this case, an impedance converter is used to convert the 75-ohm of the signal into 120-ohm, and then a video balun is used to convert the unbalanced signal into a balanced signal for output. A video balun for this purpose is known its one side provided with a Bayonet Neill-Concelman (hereinafter referred as BNC) connector for connection to an electronic video camera, monitor, video apparatus or the like, and its opposite side provided with two metal terminals for the connection of the two electrical wires of a network line. Before connection, a cutting tool must be used to cut the insulation of the two electrical wires of the network line, and then the conductors of the electrical wires are respectively fastened to the metal terminals of the video balun with a respective screw or directly bonded to the metal terminals with a solder material. This network line mounting procedure consumes much labor and time.
The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a toolless video balun, which allows quick connection to a network line without tools. According to one aspect of the present invention, the toolless video balun comprises a bottom cover shell covered with a top cover shell to hold a circuit board and a BNC connector, two metal terminals bonded to the circuit board with the respective sharp-edged top metal holder portions respectively inserted into respective insertion slot in a terminal block at the top cover shell, and a pressure cap pivoted to the top cover shell for holding down electrical wires of a network line in wire grooves in the terminal block for causing the sharp-edged top metal holder portions of the metal terminals to make contact with conductors of the electrical wires of the network line respectively.
According to another aspect of the present invention, the bottom cover shell and the top cover shell each comprise a semicircular flange. The semicircular flange of the top cover shell and the semicircular flange of the bottom cover shell are abutted against each other to hold the BNC connector firmly in place. The BNC connector has a cylindrical block disposed at its one end and set in between the semicircular flange of the top cover shell and the semicircular flange of the bottom cover shell. Further, the semicircular flange of the bottom cover shell has two engagement ribs protruding from its top wall and symmetrically disposed at two sides, and a flat surface portion disposed e between the two engagement ribs. The cylindrical block of the BNC connector has a flat bottom wall supported on the flat surface portion of the semicircular flange of the bottom cover shell, and a locating groove extending around the periphery and forced into engagement with the engagement ribs of the semicircular flange of the bottom cover shell.
According to still another aspect of the present invention, the pressure cap has one end pivoted to the top cover shell and the other end provided with at least one retaining block, and the bottom cover shell has at least one retaining hole at its one end for receiving the at least one retaining block of the pressure cap when the pressure cap is closed on the top cover shell to hold down the inserted electrical wires in the sharp-edged top metal holder portions of the metal terminals.